The present invention relates to a drive device for an elevator or a similar installation.
More precisely, the invention relates to means for controlling the up and down movement of an elevator cage or the like in the elevator shaft in which it is installed.
In the present patent application, the term "elevator cage or the like" covers not only conventional elevators for the able bodied, but also hoists and lifts for goods or for the handicapped.
It is well known that there are two major techniques in existence for implementing the drive device that controls the up and down movements of an elevator cage, which devices are either electrical or hydraulic. The present invention relates solely to the field of hydraulically controlled elevators. Naturally, the term "hydraulic" control covers means that are powered by a liquid that is not necessarily water.
In drive systems for elevators of the hydraulic type, it is conventional to have an actuator whose stroke serves to control the displacements of the elevator. The actuator cylinder is fixed in the elevator shaft and the end of the actuator rod is secured to the frame which is itself secured to the elevator cage.
It will be understood that controlling the displacement of an elevator cage in this way requires an actuator to be implemented whose stroke is very large since it is naturally equal to the displacement amplitude of the elevator cage. This makes it necessary in particular to use actuators having telescopic rods which become very difficult to make once the stroke of the elevator is large.
Nevertheless, it should be emphasized that hydraulic devices for moving an elevator cage present numerous advantages over electrically controlled devices. In particular, the cost of hydraulic drive devices for large loads is small compared with the cost of electric motor devices, and in addition such control devices are much quieter than electric motor devices. This advantage of quietness becomes particularly important when installing elevators in buildings.